1. Field of the Invention
There is a continuing effort to provide for the cloning and expression of DNA sequences. A particularly fruitful approach in obtaining DNA associated with expression products of structural genes found in genomic DNA has been the reverse transcription of messenger RNA and the cloning, manipulation and expression of the reverse transcripts of the messenger RNA. Several expression vectors have been used with various antigen screening techniques to identify recombinant DNA containing clones. However, these techniques lack the sensitivity and efficiency necessary to isolate specific recombinant molecules from cDNA libraries containing 10.sup.5 -10.sup.7 clones.
Desirable characteristics of a recombinant expression vector for screening cDNA clones include: propagation in a host cell as a single-copy genomic insert to enhance the stability of the insert containing vector and to facilitate repression of foreign genetic information; response to induction with a rapid increase in copy number and high level transcription of the foreign DNA; features providing for minimizing degradation of the foreign DNA expression product; and means for isolating the intact foreign DNA expression product.
2. Brief Description of the Prior Art
Illustrative of the use of expression vectors and various antigen screening techniques to identify recombinant DNA containing clones are articles by Skalka and Shapiro, Gene (1976) 1:65-79; Sanzey et al., PNAS USA (1976) 73:3394-3397; Erlich et al., Cell (1978) 13:681-689; Broome and Gilbert, PNAS USA (1978) 75:2746-2749; Clarke et al., Methods Enzymol. (1979) 68:436-442; and Kemp and Cowman, PNAS USA (1981) 78:4520-4524. Lambda phage are described by Williams and Blattner (1980) Bacteriophage Lambda Vectors for DNA Cloning in Genetic Engineering 2:201 (Setlow and Mullander, eds.).